A majority of motor vehicle transmissions have multiple, discrete gear ratios used to provide a mechanical advantage in powering the vehicle.
Some transmissions configured with discrete gear ratios are designed to be shifted between the ratios manually, i.e. by a vehicle operator. Other transmissions are designed to be shifted fully automatically, under the direction of a specially programmed electronic controller. There are also semi-automatic transmissions that may either be shifted entirely automatically by the controller, or whose shifting may be directed by the operator. A dual-clutch transmission (DCT) is one example of a semi-automatic type.
During design and development of a vehicle drivetrain, quality of transmission ratio changes typically commands particular attention. Such attention is generally warranted because interruption and resumption of engine torque flow during the shift may generate driveline disturbances and reduce comfort of the vehicle occupants.